The present invention relates generally to a hydraulic drive system and, more particularly, to a hydraulic drive system including a plurality of traction members individually driven by separate hydraulic drive motors.
Many work vehicles use hydraulics to control certain functions. For example, many work vehicles, such as four wheel drive articulated loaders, include hydraulic drive motors operably coupled to each wheel to drive the vehicle in motion. When the vehicle is traveling in a straight line, all four wheels move along the ground at substantially the same contact or ground speed (although the rotational speed of the rear wheels may vary relative to the rotational speed of the front wheels, depending upon their respective radii). However, when the vehicle is turning, the wheels do not move at the same ground speed. For example, when the vehicle is turning to the left, the ground speed of the right front wheel and the right rear wheel is greater than the ground speed of the left front wheel and left rear wheel, respectively, due to the greater distance from the center of the turn. As is known, the outside wheel in a turn must move at a faster ground speed than the corresponding inside wheel.
Additionally, it is known that turning wheels (i.e., those wheels which are turning or steering, whether front or rear) typically move at a faster ground speed than those wheels which are not turning. For example, if the front wheels are turning, then typically the left front wheel and right front wheel move faster than the left rear wheel and right rear wheel, respectively. In general, the left and right turning wheels move fastener than the respective left and right non-turning wheels.
As may be appreciated, to accommodate the increased ground speed of a wheel in a turn, whether an outside wheel or a turning wheel, the hydraulic drive motor associated with the faster moving wheel must likewise move faster. To do this, the hydraulic drive motor associated with the faster wheel requires more hydraulic fluid than the hydraulic drive motor associated with the slower wheel.
In some conventional work vehicles, a single hydraulic pump provides flow proportionally to multiple hydraulic motors connected in parallel. While this arrangement allows the wheels to rotate at relative variable speeds, for example, when turning, it is limited in its ability to deliver propulsion when one or more wheels lose traction. More particularly, the hydraulic fluid takes the path of least resistance in such a situation, such that all fluid flows to the wheel which loses traction, thereby causing propulsion to cease and the work vehicle to stop moving.
A differential lock in the form of a spool type flow divider may be utilized to proportion or divide the flow of hydraulic fluid from the pump to the individual drive motors. However, such spool type flow dividers typically operate efficiently only within a narrow flow range due to limitations of the divider orifices. The spool type flow divider relies on pressure developed from hydraulic flows and thereby becomes less effective at low flow rates. Moreover, the dividing function is substantially reduced, if not effectively lost, in low flow ranges. As such, a spool type flow divider may cause the loss of power to the drive motors when another vehicle function, such as steering, loading, or braking is using hydraulic fluid. Additionally, such spool type flow dividers may generate heat due to fluid flow through the orifices.
According to an illustrative embodiment of the disclosure, a vehicle includes a frame, a first traction member operably coupled to the frame, and a second traction member operably coupled to the frame. A first hydraulic motor is operably coupled to the first traction member for driving the first traction member in motion. A second hydraulic motor is operably coupled to the second traction member for driving the second traction member in motion. A hydraulic pump is fluidly coupled to the first hydraulic motor and the second hydraulic motor. A first positive displacement flow divider is positioned intermediate the hydraulic pump and the first and second hydraulic motors. The first positive displacement flow divider is configured to divide the flow of hydraulic fluid from the hydraulic pump to the first and second hydraulic motors, and to provide a differential lock so that during a first mode of operation the speed of the first hydraulic motor is substantially fixed relative to the speed of the second hydraulic motor.
Further illustratively, the hydraulic pump is a bi-directional pump including a forward port and a reverse port, wherein the forward port is fluidly coupled in series to the first positive displacement flow divider. Further illustratively, a second positive displacement flow divider is fluidly coupled in series to the reverse port of the hydraulic pump. The first positive displacement flow divider is positioned intermediate the hydraulic pump and forward ports of the first hydraulic motor and the second hydraulic motor, and the second positive displacement flow divider is positioned intermediate the hydraulic pump and reverse ports of the first hydraulic motor and the second hydraulic motor.
Further illustratively, a crossover orifice is provided in fluid communication with a fluid path from the first positive displacement flow divider to the first hydraulic motor and a fluid path from the first positive displacement flow divider to the second hydraulic motor. The crossover orifice is configured to provide a bypass so that during a second mode of operation the speed of the first hydraulic motor may vary relative to the speed of the second hydraulic motor.
According to a further illustrative embodiment of the disclosure, a vehicle includes a frame, a first traction member operably coupled to the frame, and a second traction member operably coupled to the frame. A first hydraulic motor is operably coupled to the first traction member and includes a forward port and a reverse port. A second hydraulic motor is operably coupled to the second traction member and includes a forward port and a reverse port. A bi-directional hydraulic pump includes a forward port and a reverse port, wherein the forward port of the pump is fluidly coupled to the forward port of the first hydraulic motor and the forward port of the second hydraulic motor. The reverse port of the pump is fluidly coupled to the reverse port of the first hydraulic motor and the reverse port of the second hydraulic motor. A forward rotary gear flow divider includes an inlet port, a first outlet port, and a second outlet port, wherein the first outlet port is in fluid communication with the inlet port and the forward port of the first hydraulic motor, and the second outlet port is in fluid communication with the inlet port and the forward port of the second hydraulic motor. A reverse rotary gear flow divider includes an inlet port, a first outlet port, and a second outlet port, wherein the first outlet port is in fluid communication with the inlet port and the reverse port of the first hydraulic motor, and the second outlet port is in fluid communication with the inlet port and the reverse port of the second hydraulic motor.
Further illustratively, a crossover orifice is provided in fluid communication between a fluid path between the forward rotary gear flow divider to the first hydraulic motor and a fluid path from the forward rotary gear flow divider to the second hydraulic motor. The crossover orifice is configured to provide a fluid bypass for allowing differential speed between the first hydraulic motor and the second hydraulic motor.
Further illustratively, a third hydraulic motor is connected in parallel to the first hydraulic motor. The third hydraulic motor includes a forward port and a reverse port. Similarly, a fourth hydraulic motor is connected in parallel to the first hydraulic motor. The fourth hydraulic motor includes a forward port and a reverse port.
The forward rotary gear flow divider illustratively further includes a third outlet port, and a fourth outlet port, the third outlet port being in fluid communication with the inlet port and the forward port of the third hydraulic motor, and the fourth outlet port being in fluid communication with the inlet port and the forward port of the fourth hydraulic motor. The reverse rotary gear flow divider illustratively further includes a third outlet port, and a fourth outlet port, the third outlet port being in fluid communication with the inlet port and the reverse port of the third hydraulic motor, and the fourth outlet port being in fluid communication with the inlet port and the reverse port of the fourth hydraulic motor.
According to another illustrative embodiment of the disclosure, a hydraulic circuit includes a bi-directional pump including a forward port and a reverse port, and a forward rotary gear flow divider including an inlet port connected to the forward port of the bi-directional pump. The forward rotary gear flow divider further includes a first outlet port, a second outlet port, a third outlet port, a fourth outlet port, a first gear motor in fluid communication with the first outlet port, a second gear motor in fluid communication with the second outlet port, a third gear motor in fluid communication with the third outlet port, a fourth gear motor in fluid communication with the fourth outlet port, and a shaft operably coupling the first gear motor, the second gear motor, the third gear motor, and the fourth gear motor. A first drive motor includes a forward port and a reverse port, the forward port being connected to the first outlet port of the forward rotary gear flow divider. A second drive motor includes a forward port and a reverse port, wherein the forward port is connected to the second outlet port of the forward rotary gear flow divider. A third drive motor includes a forward port and a reverse port, wherein the forward port is connected to the third outlet port of the forward rotary gear flow divider. A fourth drive motor includes a forward port and a reverse port, wherein the forward port is connected to the fourth outlet port of the forward rotary gear flow divider.
Further illustratively, a first crossover orifice is connected to the first outlet and the second outlet and is configured to provide a bypass for permitting differential speed between the first drive motor and the second drive motor. A second crossover orifice is illustratively connected to the second outlet and the third outlet and is configured to provide a bypass for permitting differential speed between the second drive motor and the third drive motor. A third crossover orifice is illustratively connected to the third outlet and the fourth outlet and is configured to provide a bypass for permitting differential speed between the third drive motor and the fourth drive motor.